CALL: DERIVATIVE


x

  A 1-dimensional array of ordinates.

  This array must be strictly in increasing order.
  This array must have the same length as y.

y

  A 1-dimensional array of function values.

  This array must have the same length as x.

x_int

  A number, the value of x at which y'(x) is to be computed.

dy

  On return, a number approximately equal to y'(x)

option

  A character string that can contain the following
  keywords:

  -------------------------------------------------------------
  Keyword       Meaning                     Notes
  -------------------------------------------------------------
  LINEAR        Linear interpolation        Rarely useful
  PARABOLIC     Quadratic interpolation     Default
  CUBIC         Cubic interpolation         Risk of oscilation
  -------------------------------------------------------------

Keyword index. Formatted on 10/11/98.